Currently available fish netting exhibits ascertainable properties for material cost, durability, and hydrodynamic drag, i.e. the netting's resistance to movement through water. For fishing trawlers, higher netting drag increases fuel consumption, and requires operating engines at higher speed which reduces engine life.
Manufacturers of conventional knotted netting try to achieve a uniform mesh throughout sheets of netting that are frequently referred to as netting panels. This uniformity includes uniformity of twines (i.e. all twines having identical physical characteristics), uniformity of mesh size, and uniformity of mesh bar length. Manufacturers frequently advertise uniformity throughout a netting panel's twines and mesh sizes as a favorable netting characteristic.
Since conventional knotted netting is a commodity product with numerous manufacturers competing in offering their products to the same group of potential purchasers, another desirable netting characteristic is that it have low manufacturing cost.
A significant operational characteristic of conventional knotted fish netting is that it fatigues during use. That is, new conventional netting loses strength after being placed in service. It has also been observed that conventional knotted fish netting almost always fails in the same way. The first observation is that conventional knotted fish netting almost always breaks at the knot which couples together two intersecting twines, a basic twine and a shuttle twine. Furthermore, it has also been observed that, depending upon the specific types of twine used in making the conventional knotted fish netting, almost always the same twine, i.e. the basic twine or the shuttle twine, breaks.
In an attempt to ensure a minimum netting strength after a specified interval of use and to thereby avoid fatigue failure, newly manufactured conventional knotted netting must be much stronger initially than the minimum strength required at the end of the netting's service life. The additional material required so conventional netting avoids fatigue failure and thus guarantees a minimum strength after a specified interval of use increases the netting's bulk which correspondingly increases the netting's drag and the cost of manufacture.
The bulk of conventional long lived knotted netting adversely affects midwater trawls and other fishing gear. A conventional midwater trawl includes a front-end and mouth which includes wings that tend to herd fish toward the center of the trawl. The aft end of the trawl's front-end connects to a back end or mid-portion jacket of the trawl. A codend or brailer bag connects to the aft end of the back end and closes the end of the trawl furthest from the front-end.
It is highly desirable to have as much volume as possible in the back end of midwater trawls to increase fish flow and water velocity flow into the brailer bag or codend, while keeping open the mesh in the netting that forms the back end of the trawl. Keeping open the mesh in netting forming the back end of the trawl also reduces bycatch, unintended catching of marine organisms. Bycatch increases if the drag of conventional netting collapses the back end of the trawl thereby preventing smaller marine organisms from passing through the netting.
A midwater trawl's back end is usually assembled from conventional machine-made knotted netting. When being towed through the water, conventional netting entrains a pressure wave in the water. The pressure wave created by the bulk of back end's netting produces what is known colloquially as a bucket effect. This pressure wave produces competing forces which act on the netting both:                1. to keep the back end of midwater trawls open thereby effectively operating analogously to a conventional sea anchor; and        2. to significantly reduce the trawl's volume due to tension in the trawl caused by the netting's drag.        
Another characteristic exhibited by currently available machine-made knotted netting is that it usually vibrates when towed through a water entrained environment similar to the flapping of a flag in the wind. The vibration experienced with conventional machine-made knotted netting can descale fish if they pass through netting rather than being caught therein, particularly if the netting is vibrating. The problem of descaling is of particular concern for pelagic and semi-pelagic species of fish.
In view of the considerations set forth above, it is clearly advantageous if netting exhibits the lowest possible drag for specified strength. Furthermore, it is highly desirable if netting, in addition to the preceding characteristics, also exhibits good:                1. elongation thereby providing the netting with load sharing across a netting panel and shock absorbing properties; and        2. resistance to fatigue failure, i.e. netting which exhibits resilience and retains its strength better throughout the netting's service life.        
Presently there exist three (3) subtly different types of conventional machine-made knotted netting. The subtle differences that occur among different machine-made knotted netting arise from the way in which netting machines knit the knots that couple immediately adjacent pairs of twines to each other. A first difference is that:                1. for two (2) types of machine-made knotted netting the same twine of a pair of immediately adjacent twines is always use for forming the same part of the weavers knot, e.g. one twine of an immediately adjacent pair of twines always forms the bight while the other twine always forms the loop; and        2. for a third type of machine-made knotted netting both twines are used alternatively, back and forth for forming respectively the bight and the loop.Within the first type of machine-made knotted netting described above:        1. in one (1) type of machine-made knotted netting the loop of the knot being always formed with the same twine also always turns in the same direction, i.e. always has clockwise or counter-clockwise; and        2. in a second type of this machine-made netting the knot's loop alternates direction between immediately adjacent pairs of knots, i.e. the direction clockwise or counter-clockwise for the loop alternates back and forth between immediately adjacent knots.Those skilled in the art frequently refer to the two different rotations for the loop, i.e. clockwise or counter-clockwise, as being either a Z-type or an S-type weavers knot. The second type of machine-made netting identified above in which the loop alternates direction tends to counterbalance twist in the twines and the finished netting, and also reduces weakening of the twines at knots.        
In addition to attempting to produce machine-made netting which doesn't twist-up, netting manufacturers also employ various techniques in attempting to improve fatigue resistance, i.e. improve the resilience, of machine-made netting. One technique used to improve fatigue resistance is incorporating a larger sized knot, e.g. double knotting, at junctures between individual twines that form the cell bars of conventional knotted netting. The principle underlying the use of larger sized knots is that intersecting twines forming larger knots have a larger bend radius which distributes load on the twines more uniformly across the twines entire cross-section. Thus, it is widely believed in the netting industry that one way to obtain a greater strength retention from a given twine used in machine-knotted netting is to increase knot size, either by doubling the twines (i.e. two parallel twines in place of one), or by making a double knot. However, while it is widely believed that the larger the knot the stronger the netting, it is also widely believed that the larger the knot, the greater the netting's drag. Consequently, this particular solution for improving fatigue failure increases netting drag in order to provide netting that is stronger and exhibits resilience.
Since fishing gear drag reduction is a significant factor in overall efficacy of a fishing operation, a decision to accept greater drag in portions of fishing gear in order to obtain greater resilience tend to be carefully balanced. Thus, the use of netting having larger sized knots is generally disfavored throughout most of a trawl net. The use of enlarged knot netting tends to be confined to limited regions of trawl nets, particularly regions that regularly incur higher loads and abrasion.
It is also a widely held belief among netting manufacturers that the greater the amount of material in the netting, for example the larger the twine diameter for a given twine density and material, that the netting must inevitably be stronger and more resilient to fatigue failure. Thus, a widely held belief is that, while smaller size twines and smaller knot sizes produce lower drag netting, they also reduce the netting's strength and resilience.
In view of the preceding considerations, due to an increasing demand for lower drag netting in the fishing industry, there presently exists a desire for knotted netting that employs a reduced knot size and reduced amount of material while remaining just as strong or even stronger than a netting which employs a larger size knot and more material.
The most widely adopted and generally viewed as most successful solutions to the preceding problems include the use of expensive superfiber materials such as ultra high molecular weight polyethylene, identified by the trademarks Dyneema® and Spectra®. Spectra is a highly modified polyethylene fiber material developed by Honeywell, Inc. that is manufactured by Allied-Signal Inc. of Morristown, N.J. Dyneema, which is similar to the Spectra fiber, is a high modulus polyethylene fiber made by DSM High Performance Fibers B.V. of Heerlen, Kingdom of Netherlands. An alternative solution to the use of superfiber materials is the use of high tenacity materials, specifically more concentrated, i.e. more drawn and thus higher tenacity, polyethylene materials.
The Dyneema and Spectra materials, rather than providing comprehensive solutions to the preceding problems, have only experienced limited use because they are substantially inelastic, and are significantly more expensive than other competing materials. Consequently, in many instances knotted netting made from Dyneema or Spectra material provide some but not all of the desirable netting characteristics summarized above. Specifically, use of knotted netting made from Dyneema or Spectra material is usually limited to applications which require high strength and, in many cases, very low drag and fatigue resistance. However, due to the poor elongation characteristics of Dyneema or Spectra materials, and the concurrent inability to distribute unbalanced loads across a netting panel, trawl nets which incorporate sheets of machine-made knotted netting made from superfibers sometimes experience fish net collapse as well as loads being borne by isolated sections of the panel which may break mesh cell bars. Dyneema, Spectra and other superfiber materials are also not widely used in larger mesh sizes in, for example, the front-end of midwater trawls. One reason that superfiber materials are not used in larger mesh sizes is that they exhibit comparatively high drag when used for forming larger size mesh.
Lastly, and significantly, netting made from superfiber materials are several times more expensive than comparable nettings made using other materials such as conventional polyethylene, nylon, polyester and so forth, and the high tenacity versions of such materials. The expense of netting made from Dyneema, Spectra and other superfiber materials limits their accessibility even to fishermen in developed nations. Consequently, nettings made from such materials are all but economically inaccessible to fishermen in underdeveloped nations, which nations account for a large portion of overall worldwide fish netting sales.
Netting made from high tenacity materials, such as more concentrated polyethylene filaments, known as high tenacity polyethylene (“HTPE”), have been successful because they exhibit higher strength than netting made with conventional materials while also providing some elongation to thereby distribute load throughout a netting panel. However, the use of modern HTPE material either already is or appears soon to be counter balanced by the fact that the relative strength of netting made from HTPE deteriorates relatively rapidly during the first twenty-four (24) hours of use. For example, commercial netting made from HTPE material available in 2001 looses sixteen percent (16%) of its initial strength during the first 24 hours of use. Conversely, a comparable netting made using HTPE material available in 1999 looses only four percent (4%) of its initial strength during the same time interval. The rate at which netting made from the two materials loose strength continues to differ throughout the remainder of netting's service life.
HTPE material's lack of resilience severely compromises its use in standard netting. One example of this limitation is that HTPE material has not been widely favored in high wear applications, such as on bottom panels of trawls. The general perception is that netting made from HTPE wears poorly. However, it appears that the rapid deterioration over time experienced with netting made from the more concentrated and thus more brittle HTPE materials is the primary reason that such netting exhibits poorer wear characteristics than those of netting made from standard polyethylene material.
In view of the preceding considerations, there exists a need for netting that exhibits low hydrodynamic drag, e.g. drag comparable to the drag of netting made from Dyneema or Spectra material, while also exhibiting the substantial elongation and lower cost of netting made from conventional nylon or polyethylene materials. Further, due to the dramatically high costs of Dyneema netting, there remains a need for a netting construction which provides strength similar to or better than that of Dyneema or Spectra netting, particularly if it provides significantly reduced material usage and cost. There also exists a need for a construction which permits netting made from HTPE materials to exhibit better resilience in comparison with netting made from HTPE materials using a conventional netting construction.